Vitamin D in human biology: exceptionally confusing in every way
Vitamin D is an extremely important category of molecules in human metabolism. However, almost every aspect/feature/parameter/function/facet of this substance - beginning with its name - is confusing.
The aim of this Post is not to solve this problem. Instead, I elaborate the nature of the confusion as thoroughly as possible, to provide a useful framework for future attempts to solve it.
Vitamin D is the only vitamin which one cannot get in sufficiency from a natural, balanced diet. Similar to iodine among micronutrients in that one can be sufficient in all else, but nonetheless deficient in this substance.
NATURE
There is confusion about the very nature of vitamin D, as an entity.
'Vitamin D' is a process, rather than a substance.
Furthermore, the effectiveness of vitamin D depends on the general health of the individual body/mind system.
TERMINOLOGY
There is confusion in all the various terms applied to vitamin D.
It is difficult to apply clearly-defined terms in the case of vitamin D. It 'falls between stools' in various ways.
vitamin?
Vitamin D qualifies somewhat as a vitamin, in the sense that it is acquired (in the form of its precursors) partly from food, and the quantities involved are small.
However, overall, 'vitamin' is something of a misnomer here.
hormone?
The end-product, namely calcitriol, functions as a hormone. However, one could not credibly refer to the precursors as hormones.
Please see https://www.perplexity.ai/search/What-is-called-_5iMhifWTV2L7J5oXXAUDA
enzyme?
It is possible that, in some of its functions, vitamin D functions catalytically. However, it hardly qualifies as an enzyme, partly because neither the precursors nor the end-product are proteins.
new category?
defiance of categorisation?
CHAIN OF PRECURSORS
The confusion is that there is no single chemical substance corresponding to the common name 'vitamin D', and this is not resolved by calling it 'hormone D'.
precursor in dermis 7-dehydrocholesterol
photosynthesised precursor cholecalciferol https://en.wikipedia.org/wiki/Cholecalciferol
form produced in liver calcefidiol https://en.wikipedia.org/wiki/Calcifediol
form produced in kidney calcitriol https://en.wikipedia.org/wiki/Calcitriol
SYNTHETIC ORGANS
The confusion is that various organs are involved in production of vitamin D, and even more diverse organs/tissues are involved in using it.
pelage (e.g. Felis catus)
dermis
liver
kidney
tissues generally
PHOTOSYNTHESIS
There is confusion in the role of light in vitamin D, including the type of light.
Ultraviolet A and B differ confusingly (from minute in 25 in https://www.bing.com/videos/riverview/relatedvideo?q=dark+horse+podcast+vitamin+D&mid=14952568900C241CD66414952568900C241CD664&FORM=VIRE)
Importance of angle of solar radiation above horizontal
Caucasians of age >70 years lose the ability to photosynthsise vitamin D
Confusion between sunburn and photosynthesis
It is confusing that Australians, with their sunny climate, seem as chronically and subclinically deficient in vitamin D as Canadians, with their boreal climate.
PARAMETERS
There is confusion among all of the various units and measures of vitamin D.
micrograms
nanograms per milliliter
nanomoles per liter
international units
FOOD
It is confusing that the only good source of vitamin D in human diets is (oily) fish, particularly given that the fishes concerned probably do not need much vitamin D themselves.
It is confusing how vitamin D gets into food chains. Does the cod, for example, photosynthesis vitamin D, or not?
https://en.wikipedia.org/wiki/Cod_liver_oil
SUPPLEMENTAL MEDIA AND DOSAGES
There is confusion in the various tablets/capsules/gummies/additives to food, and the quantities involved.
tablets
capsules
gummies
risks of overdose
relative to vitamin A
METABOLIC REACTIONS
There is confusion in the various physiological functions of vitamin D, and the continual additions to the list, as research proceeds.
functions mainly in cell-to-cell signalling
photosynthesis
consumption in immunity
epigenetic control
calcium-regulation
anti-inflammation
REQUIREMENTS
There is fundamental confusion between the human requirements of vitamin D for preventing rickets (and osteoporosis?) on one hand, and for immunity on the other.
calcium-metabolism vs facilitation of immunity
clinical vs subclinical deficiency
There is also confusion between the human species and livestock. For example, in Britain calcefidiol is freely available - and routinely administered in large quantities - in livestock husbandry, but is completely banned for the human species.
https://www.nasc.cc/pet-university/vitamin-d-deficiency-cats/
TOXICITY
There is important confusion regarding the possible toxicity of vitamin D for the human species.
from minute 11 in https://www.bing.com/videos/riverview/relatedvideo?q=dark+horse+podcast+vitamin+D&mid=14952568900C241CD66414952568900C241CD664&FORM=VIRE
used as poison for vermin
MEDICAL PRACTICE
incorporation of ongoing research into general practice
DIFFERENCES FROM OTHER MAMMALS
ORIGIN IN THE FOOD-WEB
Confusion between a common biological denominator and a vertebrate requirement that happens to have been provided by marine food-webs
marine plankton
oily fish https://www.perplexity.ai/search/Which-kinds-of-SbgnqIZCRKyhZ95ZumXmnQ
blood
milk: confusion between the minimal value for vitamin D of dairy milk in human diets and the fact that the bovine infant gets all the vitamin D it needs from its mother's milk
egg-yolk
fungi
SEQUESTRATION IN TISSUES adipose and muscle
Confusion between restoring normalcy and boosting performance
